This invention relates generally to mattress foundation structures and more particularly to a box spring assembly of a type which utilizes non-coil springs. Box spring assemblies of this general type have been known since 1964, the first such spring assembly being disclosed in U S. Pat. No. 3,286,281. Subsequently issued patents disclosing the same general type of box spring assembly are : U.S. Pat. Nos. 3,487,480; 3,506,987; 3,574,240; 3,574,241; 3,665,529; 3,680,157; 3,755,833; 3,824,639; 3,852,838; 4,060,862; 4,120,058; 4,131,961; 4,195,376; 4,218,790; 4,238,861; 4,251,892; 4,253,208; 4,339,834; and 4,470,584. Box spring assemblies of the general type shown in the above list of patents, all of which are owned by the assignee of this application, are advantageous with respect to the conventional box spring assemblies using coil springs because they provide a desired stiffer foundation for the mattress and contain a reduced amount of wire. These box spring assemblies are also advantageous from the standpoints of prolonged service life, ease of assembly, and cost of manufacture.
Additional box spring assemblies of this general type are shown in U.S. Pat. Nos. 3,546,723; 3,596,299; 3,722,013; 3,825,960, 3,833,948; 3,835,485; 3,869,740; 3,990,121; and 4,000,531.
The present invention provides a box spring assembly which utilizes a particular wire grid structure and supporting spring modules. Each spring module has a pair of vertically yieldable end portions that terminate at their upper ends in torsion bars connected by a connecting bar. The upper end torsion bars and connecting bars are clipped into the grid so as to insure a desired transmission of bedding loads over wide areas of the grid that are supported on a large number of spring modules.
This avoids localized heavy stressing of basic wire sections of the grid which are easily deformed and also helps to avoid overloading of individual spring modules, thereby insuring a prolonged service life for the box spring assembly. In addition, user comfort is enhanced by virtue of the coaction of grid and springs in reacting to bedding loads.